2,609 research outputs found
Made-to-measure galaxy models - II Elliptical and Lenticular Galaxies
We take a sample of 24 elliptical and lenticular galaxies previously analysed
by the SAURON project using three-integral dynamical models created with
Schwarzschild's method, and re-analyse them using the made-to-measure (M2M)
method of dynamical modelling. We obtain good agreement between the two methods
in determining the dynamical mass-to-light (M/L) ratios for the galaxies with
over 80% of ratios differing by < 10% and over 95% differing by < 20%. We show
that (M/L)_M2M is approximately equal to (M/L)_Sch. For the global velocity
dispersion anisotropy parameter delta, we find similar values but with fewer of
the made-to-measure models tangentially anisotropic by comparison with their
SAURON Schwarzschild counterparts. Our investigation is the largest comparative
application of the made-to-measure method to date.Comment: 14 pages, 8 figures and 5 table
Made-to measure galaxy models - I Methodology
We re-derive the made-to-measure method of Syer and Tremaine 1996, for
modelling stellar systems and individual galaxies, and demonstrate how
extensions to the made-to-measure method may be implemented and used. We
illustrate the enhanced made-to-measure method by determining the mass-to-light
ratio of a galaxy modelled as a Plummer sphere. From the standard galactic
observables of surface brightness and line-of-sight velocity dispersion
together with the h_4 Gauss-Hermite coefficient of the line-of-sight velocity
distribution, we successfully recover the true mass-to-light ratio of our toy
galaxy. Using kinematic data from Kleyna et al 2002, we then estimate the
mass-to-light ratio of the dwarf spheroidal galaxy Draco achieving a V-band
value of 539 \pm 136 M_{\odot} / L_{\odot}. We describe the main aspects of
creating a made-to-measure galaxy model and show how the key modelling
parameters may be determined.Comment: 18 pages, 15 figure
Made-to-measure galaxy models - III Modelling with Milky Way observations
We demonstrate how the Syer & Tremaine made-to-measure method of stellar
dynamical modelling can be adapted to model a rotating galactic bar. We
validate our made-to-measure changes using observations constructed from the
existing Shen et al. (2010) N-body model of the Milky Way bar, together with
kinematic observations of the Milky Way bulge and bar taken by the Bulge Radial
Velocity Assay (BRAVA). Our results for a combined determination of the bar
angle and bar pattern speed (~30 degrees and ~40 km/s/kpc) are consistent with
those determined by the N-body model. Whilst the made-to-measure techniques we
have developed are applied using a particular N-body model and observational
data set, they are in fact general and could be applied to other Milky Way
modelling scenarios utilising different N-body models and data sets.
Additionally, we use the exercise as a vehicle for illustrating how N-body and
made-to-measure methods might be combined into a more effective method.Comment: Accepted for publication, 10 pages, 7 figure
An \emph{ab initio} method for locating characteristic potential energy minima of liquids
It is possible in principle to probe the many--atom potential surface using
density functional theory (DFT). This will allow us to apply DFT to the
Hamiltonian formulation of atomic motion in monatomic liquids [\textit{Phys.
Rev. E} {\bf 56}, 4179 (1997)]. For a monatomic system, analysis of the
potential surface is facilitated by the random and symmetric classification of
potential energy valleys. Since the random valleys are numerically dominant and
uniform in their macroscopic potential properties, only a few quenches are
necessary to establish these properties. Here we describe an efficient
technique for doing this. Quenches are done from easily generated "stochastic"
configurations, in which the nuclei are distributed uniformly within a
constraint limiting the closeness of approach. For metallic Na with atomic pair
potential interactions, it is shown that quenches from stochastic
configurations and quenches from equilibrium liquid Molecular Dynamics (MD)
configurations produce statistically identical distributions of the structural
potential energy. Again for metallic Na, it is shown that DFT quenches from
stochastic configurations provide the parameters which calibrate the
Hamiltonian. A statistical mechanical analysis shows how the underlying
potential properties can be extracted from the distributions found in quenches
from stochastic configurations
Testing the nature of S0 galaxies using planetary nebula kinematics in NGC 1023
We investigate the manner in which lenticular galaxies are formed by studying
their stellar kinematics: an S0 formed from a fading spiral galaxy should
display similar cold outer disc kinematics to its progenitor, while an S0
formed in a minor merger should be more dominated by random motions. In a pilot
study to attempt to distinguish between these scenarios, we have measured the
planetary nebula (PN) kinematics of the nearby S0 system NGC 1023. Using the
Planetary Nebula Spectrograph, we have detected and measured the line-of-sight
velocities of 204 candidate PNe in the field of this galaxy. Out to
intermediate radii, the system displays the kinematics of a normal
rotationally-supported disc system. After correction of its rotational
velocities for asymmetric drift, the galaxy lies just below the spiral galaxy
Tully-Fisher relation, as one would expect for a fading system. However, at
larger radii the kinematics undergo a gradual but major transition to random
motion with little rotation. This transition does not seem to reflect a change
in the viewing geometry or the presence of a distinct halo component, since the
number counts of PNe follow the same simple exponential decline as the stellar
continuum with the same projected disc ellipticity out to large radii. The
galaxy's small companion, NGC 1023A, does not seem to be large enough to have
caused the observed modification either. This combination of properties would
seem to indicate a complex evolutionary history in either the transition to
form an S0 or in the past life of the spiral galaxy from which the S0 formed.
More data sets of this type from both spirals and S0s are needed in order to
definitively determine the relationship between these types of system.Comment: Accepted for publication in MNRAS. Version with full resolution
figure 1 can be found at
http://www.nottingham.ac.uk/~ppzmrm/N1023_PNS.accepted.pd
The Stellar Phase Density of the Local Universe and its Implications for Galaxy Evolution
This paper introduces the idea that the general mixing inequality obeyed by
evolving stellar phase densities may place useful constraints on the possible
history of the over-all galaxy population. We construct simple models for the
full stellar phase space distributions of galaxies' disk and spheroidal
components, and reproduce the well-known result that the maximum phase density
of an elliptical galaxy is too high to be produced collisionlessly from a disk
system, although we also show that the inclusion of a bulge component in the
disk removes this evolutionary impediment. In order to draw more general
conclusions about the evolution of the galaxy population, we use the Millennium
Galaxy Catalogue to construct a model of the entire phase density distribution
of stars in a representative sample of the local Universe. In such a composite
population, we show that the mixing inequality rules out some evolutionary
paths that are not prohibited by consideration of the maximum phase density
alone, and thus show that the massive ellipticals in this population could not
have formed purely from collisionless mergers of a low mass galaxy population
like that found in the local Universe. Although the violation of the mixing
inequality is in this case quite minor, and hence avoidable with a modest
amount of non-collisionless star formation in the merger process, it does
confirm the potential of this approach. The future measurement of stellar phase
densities at higher redshift will allow this potential to be fully exploited,
offering a new way to look at the possible pathways for galaxy evolution, and
to learn about the environment of star formation through the way that this
phase space becomes populated over time.Comment: 6 pages, 4 figures, accepted for publication in Astronomy &
Astrophysic
Dark-Matter Content of Early-Type Galaxies with Planetary Nebulae
We examine the dark matter properties of nearby early-type galaxies using
planetary nebulae (PNe) as mass probes. We have designed a specialised
instrument, the Planetary Nebula Spectrograph (PN.S) operating at the William
Herschel telescope, with the purpose of measuring PN velocities with best
efficiency. The primary scientific objective of this custom-built instrument is
the study of the PN kinematics in 12 ordinary round galaxies. Preliminary
results showing a dearth of dark matter in ordinary galaxies (Romanowsky et al.
2003) are now confirmed by the first complete PN.S datasets. On the other hand
early-type galaxies with a "regular" dark matter content are starting to be
observed among the brighter PN.S target sample, thus confirming a correlation
between the global dark-to-luminous mass virial ratio (f_DM=M_DM/M_star) and
the galaxy luminosity and mass.Comment: 5 pages, 2 figures. To appear in the proceedings of the IAU Symposium
244 "Dark Galaxies and Lost Baryons", Cardiff 25-29 June 2007, eds. J.I.
Davies & M.J. Disne
A dietary supplement to reduce side effects of oral isotretinoin therapy in acne patients.
AIM:
The purpose of the study was to analyze the potential capacity of a dietary supplement, based on gamma linolenic acid, vitamin E, vitamin C, beta-carotene, coenzyme Q10 and Vitis Vitifera, to reduce side effects, in particular the dry skin, erythema and desquamation, due to treatment with oral isotretinoin, and evaluate the ability of the product to increase adherence to therapy in patients with acne.
METHODS:
Forty-eight patients with nodular acne (32 females and 16 males) were randomly divided into 2 groups: 24 receveid isotretinoin therapy (20-30 mg/day) for 6 months associated to dietary supplement (twice a day), while the other 24 patients received only isotretinoin (20-30 mg/day) for 6 months. For all patients the degree of acne severity, through GAGS (Global Acne Grading System), the sebum production by Sebutape, the hydration by Corneometer and the erythema by Mexameter, were measured. We have also evaluated the adherence to treatment, asking to patients how many days a week they follow the therapy.
RERSULTS:
Patients treated with dietary supplement had lower side effects, with a less degree of erythema and dryness, and greater degree of hydration; a greater adherence to therapy was also reported.
CONCLUSION:
Thanks to antioxidant and moisturizing properties, the dietary supplement containing gamma linolenic acid, vitamin E, vitamin C, betacarotene, coenzyme Q10 and Vitis Vitifera, can be considered a useful supplement in the treatment and prevention of dry skin associated with the use of oral isotretinoin
Visible and near-infrared observations of asteroid 2012 DA14 during its closest approach of February 15, 2013
Near-Earth asteroid 2012 DA14 made its closest approach on February 15, 2013,
when it passed at a distance of 27,700 km from the Earth's surface. It was the
first time an asteroid of moderate size was predicted to approach that close to
the Earth, becoming bright enough to permit a detailed study from ground-based
telescopes. Asteroid 2012 DA14 was poorly characterized before its closest
approach. We acquired data using several telescopes on four Spanish
observatories: the 10.4m Gran Telescopio Canarias (GTC) and the 3.6m Telescopio
Nazionale Galileo (TNG), both in the El Roque de los Muchachos Observatory
(ORM, La Palma); the 2.2m CAHA telescope, in the Calar Alto Observatory
(Almeria); the f/3 0.77m telescope in the La Hita Observatory (Toledo); and the
f/8 1.5m telescope in the Sierra Nevada Observatory (OSN, Granada). We obtained
visible and near-infrared color photometry, visible spectra and time-series
photometry. Visible spectra together with color photometry of 2012 DA14 show
that it can be classified as an L-type asteroid, a rare spectral type with a
composition similar to that of carbonaceous chondrites. The time-series
photometry provides a rotational period of 8.95 +- 0.08 hours after the closest
approach, and there are indications that the object suffered a spin-up during
this event. The large amplitude of the light curve suggests that the object is
very elongated and irregular, with an equivalent diameter of around 18m. We
obtain an absolute magnitude of H_R = 24.5 +- 0.2, corresponding to H_V = 25.0
+- 0.2. The GTC photometry also gives H_V = 25.29 +- 0.14. Both values agree
with the value listed at the Minor Planet Center shortly after discovery. From
the absolute photometry, together with some constraints on size and shape, we
compute a geometric albedo of p_V = 0.44 +- 0.20, which is slightly above the
range of albedos known for L-type asteroids (0.082 - 0.405).Comment: 7 pages, 4 figures, 1 table. Accepted in A&A (June 17 2013
Liquid state properties from first principles DFT calculations: Static properties
In order to test the Vibration-Transit (V-T) theory of liquid dynamics, ab
initio density functional theory (DFT) calculations of thermodynamic properties
of Na and Cu are performed and compared with experimental data. The
calculations are done for the crystal at T = 0 and T_m, and for the liquid at
T_m. The key theoretical quantities for crystal and liquid are the structural
potential and the dynamical matrix, both as function of volume. The theoretical
equations are presented, as well as details of the DFT computations. The
properties compared with experiment are the equilibrium volume, the isothermal
bulk modulus, the internal energy and the entropy. The agreement of theory with
experiment is uniformly good. Our primary conclusion is that the application of
DFT to V-T theory is feasible, and the resulting liquid calculations achieve
the same level of accuracy as does ab initio lattice dynamics for crystals.
Moreover, given the well established reliability of DFT, the present results
provide a significant confirmation of V-T theory itself.Comment: 9 pages, 3 figures, 5 tables, edited to more closely match published
versio
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